Influential proxy advisory firm ISS recommended late Wednesday that shareholders vote for three nominees to the board of Deckers Outdoor that have been put forward by McGuire’s hedge fund, Marcato Capital.

“ISS’s recommendation validates our belief that change is needed on Deckers’ Board,” McGuire said in a statement Thursday.

ISS wasn’t always so supportive, and it took a drastic strategy shift by McGuire — who has been prodding Deckers to either sell itself or divest some of its non-core brands — for the proxy advisory firm to come around.

The hedgie had been thumping his chest for months, claiming that Deckers nine-member board needed a complete overhaul.

ISS instead urged shareholders to vote for six of Deckers’ nine nominees — only paving the way for three of Marcato’s nominees to potentially gain seats.

On Monday, with less than 10 days before the Dec. 14 shareholder vote, McGuire reduced its slate to three, saying it offered the “best chance” for a turnaround at the boot maker.

ISS’ issued its revised report in a move that was called “unusual but not unprecedented,” by Bruce Goldfarb, of proxy solicitor Okapi Partners.

“In this instance, Marcato made material changes to its slate at Deckers that were in line with the initial very specific preferences of ISS, so ISS revised its recommendation,” Goldfarb said told The Post.

Deckers meanwhile didn’t celebrate the decision.

“Deckers believes that the addition of Marcato’s nominees to the Deckers Board could result in significant disruption to the company’s ongoing successful transformation,” Deckers said in a statement Thursday.

Deckers current board still has the full support of proxy advisory firms Glass Lewis and Egan Jones.